We all use electricity every day and most of us just take it for granted that it is safe to use. Of course, for the majority of time it is. This is not usually down to luck, although when I think about some of the installations which I have seen over the years, I am well aware that on some occasions luck must have been around in abundance. Over the years the way we deal with electrical installations has changed dramatically, this is of course down to education and experience. Apart from the use of modern materials and methods of installation we also have improved legislation in place which should ensure that all installations are inspected regularly.
When I first stated full-time work back in the early 1960s, there were massive house building projects being carried out all over the country, but testing and certification of new installations was virtually unheard of. When we had completed a new domestic installation, the supply authority were really only interested in getting a signature from the person who was going to be expected to pay the electricity bill each quarter. We used to do an insulation resistance test on the meter tails and the person who installed the meter usually did the same before connection, but that was all.
The insulation resistance tester was not anywhere near as sophisticated as a modern one, we used to have to wind the handle of the instrument as it was a mini generator (Figure 1.1). I remember clearly that if for some reason we had a fault due to a nail being driven through a cable, or some other fault which resulted in a bad reading, we would just remove the fuse wire from the rewirable fuses, or disconnect the neutral of the circuit concerned before the person arrived to install the meter. That way we could be sure that the installation would be connected and that we would have an electrical supply.
It is usually easier to trace a fault if the system is live, particularly in the winter, as it is much easier to fi nd a fault in a warm house with light than a cold house in the dark. As far as earth fault loop impedance was concerned the only time we measured that was when a survey was being carried out, and again the instrument was entirely different to the equipment used today (Figure 1.2). All new houses had a copper or iron water main, as did most old ones. As you can imagine, the surface area of the metal from the water mains in contact with the soil was huge. This resulted in very low earth fault loop resistance readings.
This is because the resistance of soil is usually very low as there is such a lot of it. As the years have passed more and more electrical equipment is being installed into buildings; it is also becoming more and more sophisticated of course. Health and safety, along with insurance, has also had a hand in making it important that in the event of a fault somebody can be held responsible. Usually this will be the person signing the document to say that the installation is compliant with the current edition of the wiring regulations (BS 7671). For this reason it is very important that we take the installation of electrical wiring along with inspection, testing and certifi cation very seriously.
It is important that we not only know how to install all of our new fi xed wiring correctly, but that we know how to verify and document it as well. Not only that! We should also be able to inspect an existing installation and, with the help of some testing where required, we should be able to verify that it is fi t for continued safe use. Where damage or non-conformities are found we must be able to identify them and make sound, professional recommendations about the installation.
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